A modern-day Lascaux cave underneath Paris.

A Parisian exterminator's shop whose storefront displays stuffed rats hanging from traps.

Noirish green neon marks the location of one of the oldest private detective agencies in France.

The narrowest street in Paris.

A mud statue stands in the dark tunnels, seeming to hold up the weight of the city above.

Dedicated to the history and culture of smoking, this small museum now includes a vape lounge.

A glamorous hotel that once accommodated French resistance fighters and concentration camp survivors.

The tombstone of an unfortunate explorer who disappeared in the Paris Catacombs.

Inside a former cabaret, seven floors of erotic art.

A Belle Epoque bordello turned into a themed love hotel.

A font of vintage porn on the silver screen.

France's most famous cemetery, with some of its most curious tombs.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

Volcanic rocks ground down into sand make this Spanish beach as black as night.

Mysterious Spanish catacombs of unknown origins.

A science fiction-inspired apartment building designed by a famous Spanish architect.

Partially collapsed lava tube and cave system complete with concert hall, underground pond, and unique albino crabs.

One of the largest ossuaries in Spain is packed from floor to ceiling with bones.

This magical space partly designed by Antoni Gaudi is one of the best examples of romantic gardening in the Mediterranean.

Cliffside houses provide a spectacular view from their perch above the valley.

The chefs at El Diablo use heat generated by an active volcano to cook the food.

A once grand hotel now sits eerily abandoned in the Catalan countryside outside Barcelona.

An isolated village literally built into the crevices and rock formations of a mountain.

A completely underwater art museum sends a stark message about humans' impact on the environment.